The American Cancer Society estimates more than 180,000 new breast cancer diagnoses and more than 40,000 deaths from breast cancer in the United States in about one year. Mammography is a useful screening tool for detecting breast cancer, reducing mortality by about 25%, but is limited by a large number of false positive tests resulting in unnecessary biopsies and, more importantly, a considerable number of false negative tests resulting in missed diagnosis of cancer. In the last few years it has become apparent that nuclear medicine techniques have the potential to play an important role in the diagnosis and treatment of patients with breast cancer. Positron emission tomography (PET), using [18F]fluoro-2-deoxy-D-glucose (FDG) as a tracer of tumor glucose metabolic activity, is an accurate, non-invasive imaging technology, which probes tissue and organ function. This provides information, which is complementary to the structural image obtained from mammography. Whole body PET is a well established technology, however it is expensive, and of limited availability. Furthermore, the spatial resolution is 8-16 mm, insufficient for accurate detection and imaging of smaller tumors. The extension of PET to small, more widely available, higher spatial resolution (<3 mm) systems optimized for breast cancer imaging has the potential to save many lives. Therefore, we have designed this PET system for dedicated breast imaging. However, it can be used for full body PET and has many other uses as described above, in section on Field of Invention.
For the reasons of cost and availability it is unrealistic to expect nuclear medicine techniques to be used for mass screening. There are, however, several important situations in which the results from mammography can be unsatisfactory, and the availability of a functional imaging technique to provide additional diagnostic information would be extremely helpful. These situations include:    1. Imaging of young women with very dense breasts (where mammograms are often of poor quality and the detection of early stage breast cancer is difficult and inaccurate).    2. Imaging in women with silicone breast implants (these have high radiodensity and breast displacement is not always possible or effective).    3. Imaging in women with widespread fibrocystic changes.    4. Screening for post-lumpectomy tumor recurrence—the number of women opting for breast conservation is increasing, and functional imaging techniques, particularly the use of FDG with PET, have been shown to be extremely good at differentiating recurrent tumor from scar tissue or radiation necrosis.
Encouraging preliminary studies have already been carried out using [99mTc]sestamibi with conventional gamma cameras and 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) with whole-body PET scanners. The role of functional imaging in breast cancer, however, goes far beyond diagnosis. It is possible that PET techniques could become fundamental in predicting and monitoring the effectiveness of therapy, in particular chemotherapy and hormonal therapy. Metabolic activity as measured by FDG PET has been shown to be a more sensitive indicator of tumor response than anatomical techniques. This would allow early response to treatment to be identified and the chemotherapeutic regimen altered in the absence of a response. In addition, PET can be used to assess the concentration of estrogen receptors using the estrogen derivative [18F]fluoroestradiol. The concentration of estrogen receptors is an important predictor of the outcome of hormonal therapy.
In the future, chemotherapeutic agents could be directly labeled with positron emitters and given in trace amounts to predict response prior to the use of pharmacological levels. This might allow tailoring of the drug regimen to the individual patient, leading to a reduction in the costs and morbidity of ineffective treatments. Further interesting possibilities involve labeling monoclonal antibodies directed against breast tumor cells with 124I. This long-lived tracer would allow the distribution of antibodies to be visualized prior to therapy